Fiber is a well known nutrient, but not well understood. Put simply, fiber refers tocarbohydrates that cannot be digested by humans. They are classified as either soluble or insoluble, depending on whether they dissolve in liquids.

Insoluble fibers function mostly as bulking agents and are not very interesting. However, soluble fiber can havepowerful effects on health and metabolism (

Different types (species) of bacteria play important roles in various aspects of health, including weight management, blood sugar control, immunity and even brain function (

This is where fiber (mostly soluble) steps in. It passes through the digestive system mostly unchanged, eventually reaching the friendly bacteria in the intestine that end up digesting the fiber and turning it into usable energy.

Fiber does not get digested and tends to reach the large intestine relatively unchanged. There, certain soluble fibers can help feed the friendly bacteria that are absolutely essential for good health.

Just to clarify, acute (short-term) inflammation is beneficial as it helps the body fight foreign invaders and repair damaged cells. However, chronic (long-term) inflammation becomes a major problem when it is inappropriately deployed against the bodys own tissues.

Viscous soluble fibers such as pectins, β-glucans, psyllium, glucomannan and guar gum all thicken in water, forming a gel-like substance that sits in the gut (

This gel slows down the emptying of the stomach and increases the time it takes to digest and absorb nutrients. The end result is a prolonged feeling of fullness and a significantly reduced appetite (

Bottom Line: Fibers with a high viscosity have been shown to increase satiety, reduce appetite and cause automatic weight loss. Fibers with low viscosity appear to have no influence.

While these isolated fibers may have some health benefits, the evidence for weight control is mixed and pretty unconvincing. A very large review study found that psyllium and guar gum (both soluble, viscous fibers) are ineffective as weight loss supplements.